BlissMessage is an iPhone app which lets you send free text messages from iPhone to iPhone and from the web to iPhones as well. It leverages push notifications for instant delivery of the messages. While the basic use case is sending free text messages to other users, you can also get notified about your Twitter replies and mentions if you enter your Twitter name in the profile.

Easy and performant integration of mature MQ technologies (ActiveMQ). Java is a high-performant language to fall back on in case, and it's safer for me to code Java than C

Multi-language high-performance online dictionary designed to serve millions of search requests a day. The system combines high-quality content by the renowned dictionary publisher PONS with content generated by the web's crowd intelligence. The scalable system is developed and hosted by finnlabs.

To share large in-process caches and lucene indeces between multiple rails instances and to reuse Java libraries.

TriSanoâ„¢ is an open source, citizen-focused surveillance and
outbreak management system for infectious disease, environmental hazards, and
bioterrorism attacks. It allows local, state and federal entities to track, control and
ultimately prevent illness and death.

Extensive roadmap - didn't think Ruby alone could get it done and want to fall back
to Java rather than C.